1. Field of the Invention
The present invention relates generally to telecommunications. More particularly, the present invention relates to voice band modems which transmit information utilizing signals with low frequency components.
2. State of the Art
Certain types of voice band modems, such as V.90-type and V.92-type modems transmit information utilizing signals with essential contents which include low frequency components (close to DC). In particular, these modems utilize a spectrum which includes the frequency region of power supply tones and their harmonics, which may have significant detrimental effect on modem performance. A very important practical case is when, for information transmission, the modem requires using the same frequencies as the common power supply frequencies of e.g., 50 Hz (Europe) or 60 Hz (USA) and/or their harmonics.
Dealing with this kind of interference is not straight-forward. It is not desirable to just filter out the low portion of the spectrum to get rid of the interfering frequencies (hereinafter referred to as “interferers”) because the signal itself utilizes the same frequency range.